1. Field of the Invention
The present invention relates to a semiconductor photo-sensor used for a light intensity detection device, and more particularly to a semiconductor photo-sensor which uses a semiconductor photo-sensor as a photo-sensor.
2. Related Background Art
In many prior art semiconductor photo-sensors, photo-conductive elements are used as photo-sensors because they provide a large output, do not need amplifiers and can be produced with a low manufacturing cost. The conductivity of photo-conductive element changes with light illumination, and the change is converted to a current or a voltage for signal processing.
However, the photo-conductive element has a low sensitivity and 0.1-1 lux is a limit for measurement. Since a photo-sensor needs a relatively large area, it is difficult to measure an illumination of a small spot area having dimensions such as several hundreds microns because of this low sensitivity or because of low S/N ratio.
A semiconductor photo-sensor which converts an optical signal to an electric signal comprises a photo-sensor and a signal processing circuit and is constructed according to one of the following two methods.
One construction comprises a single photo-sensor of a relatively large area and a signal processing circuit formed on one semiconductor substrate. The other construction has a plurality of divided photo-sensors formed on one or more semiconductor substrates and signal processing circuits for the photo-sensors formed on other semiconductor substrate, the substrates being connected by wire bonding.
In the former construction, since the optical signal for different positions of a detection plane of the photo-sensor are averaged, it is difficult to simultaneously detect two different optical signals simultaneously applied to different positions on the detection plane, and the effect of external light is large when the optical signal is applied to a portion of the detection plane. In the latter construction, the number of semiconductor substrates increases, packaging area, increases, signal current leaks from the bonding area and the sensitivity is lowered.